Cryosorption pumps, whether cooled by open or closed cryogenic cycles, generally follow the same design concept. A low temperature array, usually operating in the range of 4.degree. to 25.degree. K, is the primary pumping surface. This surface is surrounded by a higher temperature radiation shield, usually operated in the temperature range of 70.degree. to 130.degree. K, which provides radiation shielding to the lower temperature array. The radiation shield generally includes a housing which is closed except at a frontal array positioned between the primary pumping surface and the chamber to be evacuated. This higher temperature, first stage frontal array serves as a pumping site for higher boiling gases such as water vapor or carbon dioxide. Cryosorption pumps are conventionally quite bulky and cumbersome due to the refrigeration equipment necessary to produce the requisite cryogenic cooling.
Heretofore, mechanical rotary vane and piston type pumps capable of producing intermediate pressures (0.01 to 10 torr) have been used as backing pumps for oil diffusion and turbomolecular pumps as well as roughing pumps for starting ion pumps and cryogenic pumps. These pumps are generally quite heavy, bulky and usually produce oil vapors which can contaminate a vacuum system. Such pumps also are quite energy inefficient.
Molecular sieve materials have been used to both produce high vacuums when cooled to very low temperatures (less than 20.degree. K) and have been used in intermediate vacuum applications (when cooled to approximately 70.degree. K, or at room temperature under special conditions).
Previous use of molecular sieve materials for intermediate pressure sorption pumping have relied on either the use of a replaceable cold material such as liquid nitrogen or a very bulky and heavy closed cycle refrigerator to cool the molecular sieve material down to the necessary pumping temperatures. The use of such molecular sieve materials for achieving intermediate pressure sorption pumping has generally been reserved for very clean vacuum roughing applications.
Portable instrumentation requiring the use of intermediate pressure vacuum pumping has generally relied upon the use of heavy and bulky mechanical pumps, due to the difficulty involved in obtaining liquid nitrogen for cryosorption pumps under field conditions, and also due to the size and weight of room temperature sorption pumps.
The present invention relates to a miniature cryosorption pump which is an improvement over prior art cryosorption pumps.